The present invention relates to the use of ultrasound testing to detect anomalies in wooden members. More specifically, the present invention relates to the use of a roller device housing an ultrasonic transducer element array for the ultrasound testing of wooden members.
The grading of wooden members is important to the entire lumber and construction industry. Accurate grading allows a builder to match the strength of the wooden member to the type of construction project. In addition, proper grading permits a sawmill to charge a premium for stronger members, while dedicating weaker members for more appropriate tasks. Grading techniques have been developed that nondestructively measure certain physical properties of wooden members. One such technique uses ultrasonic waves to measure physical properties.
Ultrasound measurement systems often use rolling transducers to detect anomalies in, and thus the strength of, the wooden member. By passing an ultrasonic wave of known characteristics through the wooden member, the system is able to detect anomalies by analyzing a modification of the wave after it passes through the member. Specifically, a transducer located on one side of the wooden member directs an ultrasonic wave through the member to another transducer located on the opposite side of the wooden member. When part of the ultrasonic wave passes through the anomaly, it is modified and collected by a receiving transducer. A computer connected to the receiving transducer compares the transmitted wave with the wave that was passed through the wooden member, or with some xe2x80x9cstandardxe2x80x9d or xe2x80x9cidealxe2x80x9d wave. Based on the distorted difference between the two waves, the computer displays the anomalies on a monitor. Moreover, the system may be able to determine the type of anomaly (e.g., knots, checks, or split), its location, and its effect on the strength of the wooden member.
The demanding production line requirements of today""s sawmill require that multiple characteristics of the wooden member be determined simultaneously. For structural softwood lumber and hardwood pallet stock, for example, the ultrasound measurement system must determine the location and severity of a knot at the same time it searches for other anomalies, like splits or checks (i.e., internal voids). In order to map out defects, multiple transducer systems have been used to produce rough maps of defect locations. In order to expand the coverage of the wooden members in such multiple transducer systems, the multiple transducers are staggered along the direction of movement of the wooden member (z direction), as illustrated in prior art FIG. 1A. Due to mechanical mounting clearance requirements, the transducers are staggered in the z direction and not aligned along the y axis, thereby preventing any benefits from redundancy in geometry.
Those skilled in the art will appreciate that the presence of multiple transducers creates certain operational problems. Obviously, the use of multiple individual transducers increases the mechanical complexity of the ultrasound measurement system. Also, the transmitting transducers must be separated physically from each other to allow for mechanical mounting clearance. However, this required separation of the transmitting transducers and their dedication to one receiving transducer means that certain smaller anomalies, like splits, may fall between the ultrasound waves, thus foiling detection.
FIGS. 1A and 1B provide an example of such a prior art multiple-transducer ultrasound measurement device 100 for grading a wooden member 107. As will be understood from the following description, the term wooden member includes logs, cants, lumber, boards (like structural softwood lumber and hardwood pallet stock), and wood composites in various stages of processing. FIG. 1A is a perspective view of prior art multiple-transducer ultrasound measurement device 100. As shown in FIG. 1A, multiple-transducer ultrasound device 100 includes three transmitting transducers 101-103, located adjacent to each other. Multiple-transducer ultrasound device 100 also includes three receiving transducers 104-106. Although FIG. 1A shows three transmitting transducers 101-103 and three receiving transducers 104-106, it should be appreciated that multiple-transducer ultrasound device 100 may include any number of receiving and transmitting transducers. Wooden member 107 is located between transmitting transducers 101-103 and receiving transducers 104-106.
Transmitting transducers 101-103 are separated from each other by some distance d along the z-axis. Distance d provides the necessary physical separation so that transducers do not physically interfere with each other. Receiving transducers 104-106 also are separated from each other by a distance d equal to distance d for the same reason. Separating receiving transducers 104-106 by distance d, equal to d, places receiving transducers 104-106 in the same x-axis plane as transmitting transducers 101-103. Because of this, transmitting transducer 101 communicates exclusively with receiving transducer 104, transmitting transducer 102 communicates exclusively with receiving transducer 105, and transmitting transducer 103 communicates exclusively with receiving transducer 106.
FIG. 1B is a front-view of prior art multiple-transducer ultrasound measurement device 100, further detailing communication between transmitting transducers 101-103 and receiving transducers 104-106. In operation, as wooden member 107 moves along the z-axis, transmitting transducers 101-103 roll along one side of wooden member 107, and receiving transducers 104-106 roil along the opposite side. Transmitting transducers 101-103 transmit ultrasonic waves through wooden member 107 to receiving transducers 104-106. Anomalies within wooden member 107 affect the transmitted waves as they pass through wooden member 107 (as discussed further with reference to FIG. 3). By analyzing the anomaly-affected waves received by receiving transducers 104-106, as compared to the transmitted waves or a xe2x80x9cstandardxe2x80x9d wave (as discussed further with reference to FIG. 6), multiple-transducer ultrasound device 100 is able to provide an output that characterizes the various anomalies.
As shown in FIG. 1B, each of transmitting transducers 101-103 communicate exclusively with receiving transducers 104-106, respectively. In particular, transmitting transducers 101 sends an ultrasonic wave 110 to receiving transducer 104, transmitting transducers 102 sends an ultrasonic wave 111 to receiving transducer 105, and transmitting transducers 103 sends an ultrasonic wave 112 to receiving transducer 106. Notably, each of waves 110-112 travel in the x-direction, perpendicular to transmitting transducers 101-103, receiving transducers 104-106, and wooden member 107. Because each receiving transducer 104-106 captures wave 110-112, respectively, exclusively from one transmitting transducer 101-103, respectively, portions of waves 110-112 that stray beyond their assigned receiving transducer 104-106 are ignored. As a result, small anomalies 108 and 109 that lie on the periphery of each transducer transmitter/receiver pair 101/104, 102/105, and 103/106 may go undetected.
The solution of FIGS. 1A and 1B is depicted by Fry et al. in U.S. Pat. No. 5,237,870, where Fry et al. describe multiple, independent ultrasound transducers (Fryxe2x80x94FIGS. 11 and 12). Each transducer collects ultrasound information from a single aspect along the wooden member. Specifically, the information is collected along a linear arrangement of measurement points on a face of the member. Similarly, the publication xe2x80x9cUltrasonic defect detection in wooden pallet parts for quality sortingxe2x80x9d (Schmoldt, D. L, R. M. Nelson, and R. J. Ross 1996. In S. Doctor, C. A. Lebowitz, and G. Y. Baaklini (eds.) Nondestructive Evaluation of Materials and Composites, SPIE 2944: 285-295) describes multiple measurements taken along the face of a board in order to create an xe2x80x9cimagexe2x80x9d of the ultrasound properties, which are then correlated to physical properties.
There are several drawbacks in the prior art. First, the use of multiple individual transducers increases the complexity of the mechanical system as more transducers are used, for example, to increase the positional resolution of the system. As evidenced from the depictions in Fry et al., as the number of scan lines across the board increases, it is necessary to increase the number of transducer mechanisms. Because the transducers must be physically separated from one another, this requires that the transducers be spaced along the length of the wooden member. This increases the length of the mechanical system, thus further complicating it and increasing the cost.
Further, the arrangements proposed in the prior art may not be sensitive to defects, such as splits, which are of very narrow extent in the direction of the scan lines. That is, these features often may be completely between the scan lines, and therefore be undetectable by the methods described. Any feature which is significantly smaller than the ultrasound beam may also be undetectable using the methods of the prior art. As an example, because splits are often very narrow, even if a split falls directly in line with a scan line, it may be missed because the ultrasound energy will travel undisturbed on either side of the split, making it undetectable.
Therefore, there is a need to provide a more thorough system for detecting anomalies in wooden members.
The present invention provides a method and system for detecting anomalies in a wooden member. The method transmits ultrasonic waves of known characteristics from a first transducer in a first array of transducers through the wooden member, and receives the ultrasonic waves with more than one of a second array of transducers. The characteristics of the ultrasonic waves may include total energy, spectral energy distribution, temporal energy distribution, phase, and/or time of flight. The method may further comprise comparing at least one characteristic of the ultrasonic waves received by the second array of transducers with at least one corresponding characteristic of the ultrasonic waves transmitted by the first transducer, in order to identify abnormalities in the wooden member. Alternatively, the method may comprise determining a standard set of measurements by transmitting the ultrasonic waves from the first transducer through an acceptable wooden member, such as clear wood, or through a plastic element. At least one of the standard set of measurements may then be compared with at least one corresponding measurement of the wooden member, in order to identify abnormalities. In either case, the method may allow the wooden member to be graded based on the identified abnormalities.
The present invention further provides an apparatus for detecting anomalies in a wooden member. The apparatus includes a first roller device comprising a first array of transducers, and a second roller device comprising a second array of transducers. A first transducer in the first array of transducers communicates with more than one transducer in the second array of transducers. The apparatus may be designed such that the wooden member may pass between the first roller device and the second roller device. In addition, the first array of transducers and the second array of transducers maintain an orientation perpendicular to the moving direction of the wooden member as the first roller device and the second roller device roll along the wooden member. Each of the transducers operate in an ultrasonic frequency range. Also, each transducer in the first array of transducers is acoustically isolated from each other transducer.